The United Nations has analyzed all the data, and in a new report states unequivocally that humans are the primary cause of climate change worldwide.
Compiling four potential scenarios based on varying amounts of greenhouse gas emissions and atmospheric concentrations, the Intergovernmental Panel on Climate Change announced its results and released a draft of its five-year report on the state of the global climate.
“It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century,” said the Intergovernmental Panel on Climate Change, which conducted the analysis, in a statement announcing the release of its report, Climate Change 2013: the Physical Science Basis. “The evidence for this has grown, thanks to more and better observations, an improved understanding of the climate system response and improved climate models.”
Among the most alarming findings are that the atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years, the panel said, with carbon dioxide concentrations up by 40 percent since pre-industrial times—mainly from fossil fuel emissions, as well as from emissions due to changes in net land use. About 30 percent of the carbon dioxide has been absorbed by the oceans, where it contributes to ocean acidification, the panel said.
“Observations of changes in the climate system are based on multiple lines of independent evidence,” said Qin Dahe, Co-Chair of the panel’s main working group. “Our assessment of the science finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and the concentrations of greenhouse gases have increased.”
Out of four potential scenarios, the panel calculated that by the end of the 21st century, global surface temperatures may very well increase by 1.5 degrees Celsius or even 2 degrees Celsius beyond what they were from 1850 to 1900, said Thomas Stocker, the working group’s other co-chair.
“Heat waves are very likely to occur more frequently and last longer,” Stocker said in the statement. “As the Earth warms, we expect to see currently wet regions receiving more rainfall, and dry regions receiving less, although there will be exceptions.”
Changes in the climate system since 1950 “are unprecedented over decades to millennia,” the statement said, emphasizing that “warming in the climate system is unequivocal” and that “each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850.”
Not only are these changes taking place, but they are also accelerating, the scientists cautioned.
“As the ocean warms, and glaciers and ice sheets reduce, global mean sea level will continue to rise, but at a faster rate than we have experienced over the past 40 years,” said Co-Chair Qin Dahe.
This is not news to the Indigenous Peoples of Turtle Island and beyond, of course. Already numerous indigenous communities face the effects of rising sea levels, melting permafrost and other environmental effects.